1. Technical Field
The present invention relates to a polarization element, a method for manufacturing the same, a liquid crystal device, and an electronic apparatus.
2. Related Art
Liquid crystal devices are used as an optical modulator of various electro-optic devices. Such structure of liquid crystal devices are widely known that a liquid crystal layer is sandwiched in between a pair of substrates that are disposed in an opposed manner. The devices are commonly provided with a polarization element and an alignment film. The polarization element allows predetermined polarized light to enter the liquid crystal layer, and the alignment film controls an alignment of liquid crystal molecules when no voltage is applied.
As a polarization element, a film type polarization element and a wire grid type polarization element are known. The film type polarization element is manufactured such that a resin film is extended in one direction so as to align components of the resin film in an extending direction. The wire grid type polarization element is structured such that nanoscale metal thin wires are laid over a transparent substrate. Especially, the wire grid type polarization element can be built in a liquid crystal device, thereby being considered to be effective for thinning the liquid crystal device.
However, the metal thin wires provided to the wire grid type polarization element are too fragile to be damaged even by slight contact, being very hard to be handled. For example, in a process for manufacturing a liquid crystal device in which a wire grid type polarization element is included, a polyimide film is formed on a surface of the polarization element so as to form an alignment film. The alignment film is formed by performing a rubbing treatment with respect to the surface of the polyimide film in a predetermined direction. In this rubbing treatment, the metal thin wires may be disadvantageously damaged. Therefore, the metal thin wires have to be properly protected so as not to be damaged.
Here, optical characteristics of the polarization element are affected by a material disposed between the metal thin wires, and a preferable refractive index is 1. Namely, it is best to fill between the metal thin wires with air (or to be vacuumed). Therefore, if gaps between the metal thin wires are completely filled with a protection material such as transparent resin for protecting the polarization element, the optical characteristics may be deteriorated.
JP-T-2003-519818 as a first example and JP-T-2005-513547 as a second example disclose a method for solving these problems. Namely, the method is such that a transparent substrate serving as a protection member is disposed in a manner being opposed to a forming surface of metal thin wires so as to prevent the metal thin wires from being damaged. Further, JP-A-2007-17762 as a third example discloses such method that a protection layer is formed on an upper surface of metal thin wires by sputtering so as to protect the metal thin wires.
However, the method disclosed in the first and second examples has such problem that the thickness of the whole of the polarization element is increased because of the transparent substrate used as the protection member for the metal thin wires. In a case of building the polarization element in a liquid crystal device, the thickness of the protection film disadvantageously prevents the device to be thinned. Further, the method disclosed in the third example employs a sputtering method by which a film is slowly formed, so that it takes long period of time to form the protection film having enough thickness. In addition, in the method, the upper surface of the metal thin wires is protected but the metal thin wires themselves are not reinforced, so that the wires are damaged in the rubbing treatment described above.